When a mobile terminal such as a mobile phone or the like moves from the cell of a base station to the cell of another base station in a cellular radio communication system, the mobile terminal switches its connection from the base station to the other base station through handover in order to maintain the communication.
In such a cellular system, communication performance in a cell is limited by interference within the cell itself, interference from another cell (i.e., inter-cell interference), and the like. Therefore, as a scheme for frequency reuse between cells, for example, a long term evolution (LTE) communication technology that is currently standardized in the third generation partnership project (3GPP) employs a “one-cell reuse scheme” using the same frequency in neighboring cells. According to the one-cell reuse scheme, a frequency bandwidth for each cell increases, and therefore enhancement of throughput is expected. However, inter-cell interference increases, whereby deterioration of throughput is caused, in particular, to a mobile terminal located at an edge of a cell (hereinafter also referred to as “cell edge”).
In order to reduce such deterioration of throughput, the LTE communication technology employs an inter-cell interference coordination (ICIC) technique based on a fractional frequency reuse (FFR) scheme that allocates a mobile terminal located at a cell edge a frequency different from those used in neighboring cells, or another scheme.
There have been proposed the aforementioned FFR inter-cell interference coordination technique, a handover procedure in which interference is suppressed based on information received from a cell through inter-base station communication, and the like. Please see the following literatures.    Japanese Laid-open Patent Publication No. 2007-295318    3GPP TR25.913    3GPP TR36.913    3GPP TS36.423    D. Aziz, R. Sigle, “Improvement of LTE Handover Performance through Interference Coordination,” Proc. VTC2009 spring, 2009.
Handover of a mobile terminal is typically carried out at a location near a cell boundary between a handover source base station and a handover destination base station. Thus, communication between the handover source base station and the mobile terminal is susceptible to interference from the handover destination base station, and communication between the handover destination base station and the mobile terminal is susceptible to interference from the handover source base station. Such interference causes deterioration in reception quality of the communication between a base station and a mobile terminal, so that the handover of a mobile terminal suffers from the technical problem that a control signal for handover is less likely to be properly received. When a control signal is not received properly, handover may not be successfully completed, so that communication of the mobile terminal may be disconnected.
According to the aforementioned FFR scheme, one base station allocates a frequency band for which a low transmission power is set by another base station, for communication with a mobile terminal located near a cell boundary with the cell of the other base station. This leads to a reduction in interference from the other base station that has the strongest inter-cell interference in a location near the cell boundary. However, according to the FFR scheme, a frequency allocated to a mobile terminal located at a cell edge is statically or quasi-statically set within a preset bandwidth. Therefore, a frequency band or other radio resources are not sufficiently ensured depending on the quantity of mobile terminals to be handed over, and therefore, the FFR scheme may not exhibit its advantageous effects sufficiently.